The importance of determination of the amount of blood lost by a patient undergoing a surgical operation, human or animal, is well documented. Thus, the need for simultaneous and subsequent transfusions, anesthesiology and recovery measures, subsequent therapeutic treatments, and post-operative diagnosis and prognosis, are all dependent, to at least some degree on obtaining an idea of the amount of blood lost by a patient during an operation. The greater the amount of blood lost or potential amounts of blood to be lost, the greater the need for accurate determination of actual blood lost during the procedure. Simultaneously, however, the greater the actual amount of blood lost by the patient, the less accurate estimates by those in the operating theater, including the surgeon and anesthesiologist, become. Thus, determinations of the need for transfusions and the like become increasingly difficult as operations involving high degrees of blood loss are encountered.
Another difficulty stems from the fact that the patient's current hemoglobin concentration does not accurately reflect the patient's remaining oxygen-carrying capacity. Administration of intravenous fluids may tend to diminish the hemoglobin values, and blood loss alone will not affect the concentration significantly until many hours later.
Simultaneously, the nation's blood supply has been severely threatened. Thus, the increase in AIDS, as well as traditional contaminating factors, such as HBV, have limited the available blood supply, and also pose increasing hazards to those receiving a transfusion. This highlights the need to have an accurate determination of the amount of blood lost, to determine the need for a transfusion, and if such a need is determined, exactly the quantity of transfusion to be contemplated.
U.S. Pat. No. 4,773,423 describes a method for determining blood loss. In the described process, blood is collected via a vacuum tubing, and blood is urged from collected swabs and the like, and thereafter the amount of blood lost is determined on the basis of hemoglobin content. The process presents two problems. Initially, it is noted that it is difficult, by direct vacuum suctioning, to obtain all of the blood lost by the patient. Particularly during lengthy preparations, large amounts of blood may be deposited on instruments, lost in absorbent pads, sponges and the like, which are difficult to remove on mere urging. U.S. Pat. No. 4,773,423 does not describe the method for obtaining close to 100% of the blood lost in this method. Moreover, the method described in U.S. Pat. No. 4,773,423 relies on direct color measurement of the reagent solution. Such direct measurement is difficult, particularly in light of the fact that hemoglobin is generally a mixture of varying forms, each with its own absorption spectrum, and any fluid obtained from a patient will also be complicated by a variety of dissolved and solid impurities, and debris, presenting a high degree of turbidity, and complicating direct colorimetric measurement. Alternate forms, based on measuring iron content and the like, may not give a true reading, because of the likelihood of the presence of iron in the patient's tissues, and materials employed i the operating theater.
To a similar end, a blood-loss monitor is described in the Lancet, Oct. 8, 1977, which calls for the washing of swabs and drapes on which blood is collected, followed by photocolorimetry. Again, no method is provided for directly reading hemoglobin content. Experience has demonstrated that such direct colorimetry gives unreliable values.
Accordingly, it remains a goal of those of ordinary skill in the art to provide a method for determining blood loss of a patient undergoing a surgical operation, on a real time or real time plus no more than five-minute basis, that is not dependent on direct colorimetry, or other uncertain measurements.